IME, uninstalling drivers isn't necessary anymore, whether you're using DDU or the normal uninstaller. I've changed between various Legacy DX9/10/11 and modern GPUs from both AMD and Nvidia on the same Win10 PCs, and I've never encountered a driver issue when changing graphics cards.
Windows 10 simply doesn't find compatible hardware from the get go, then fetches a proper driver itself from Windows Update, though it's often an older driver, and voila, it's working.
I don't remember any issues changing drivers on Windows 7 either. The only thing I remember could be problematic was changing motherboards, which has also worked without issues in Win10.